Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing a first embodiment of the new design;

FIG. 2 is a front view of a display screen or portion thereof with a graphical user interface showing a second embodiment of the new design; and,

FIG. 3 is another front view of FIG. 1, but showing alternative broken line subject matter.

The broken lines shown in the drawings illustrate portions of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 